Rush (The Game Book 1) by Eve Silver

Sixteen-year-old Miki Jones is pulled from her everyday life into an alternate reality game where she and a team of other teens battle the Drau—beautiful and deadly alien creatures bent on mankind’s destruction. There are no dry runs, no boot camp, no time to acclimate to new weapons. There’s only the mission: kill or be killed. Make it out alive, and Miki gets to respawn back in her real world . . . but only until she’s pulled into the terror of the game again and again.

The team’s mysterious leader insists it’s every player for herself. Other players whisper about hit points and health bars and a way out of the game. Everyone has secrets. Everyone lies. And when the mission takes a deadly turn, Miki’s only hope for survival depends on her figuring out who—and what—to trust.